Method for preparing magnetic abrasive material by supercritical carbon dioxide assisted plasma spray
Technical Field
The invention relates to the field of metal matrix composite materials, in particular to a method for preparing a magnetic abrasive material by supercritical carbon dioxide assisted plasma fusion.
Background
Compared with the traditional polishing and grinding technology, the magnetic abrasive finishing has remarkable advantages when applied to the processing of parts with extreme manufacturing characteristics (extreme structures, surfaces with complex shapes, difficult-to-process materials) due to the characteristics of unique material removal mechanism, flexible contact processing mode, excellent surface characteristics, extremely small processing stress, convenient automatic control and the like.
As a "grinding tool" in the finishing process of magnetic abrasive, the magnetic abrasive plays a decisive role in the processing efficiency and the processing quality, and the magnetic abrasive is a composite material consisting of a ferromagnetic phase and an abrasive grain phase. The ideal magnetic abrasive material has good mechanical properties (strength, hardness, toughness, stability, etc.), strong soft magnetic properties (magnetization, demagnetization, etc.), and the following characteristics: the shape is spherical and the grain diameter is consistent, the abrasive grain phase is uniformly distributed on the surface layer and the height is basically the same, the abrasive grain phase and the ferromagnetic metal matrix have stronger binding force, and the cutting edge of the abrasive grain phase protrudes outside and has self-sharpening property.
At present, the method for preparing the magnetic abrasive mainly comprises the following steps: mechanical mixing, bonding, composite coating, sintering, casting, plasma melting, atomization and rapid solidification and the like. However, the mechanical mixing method and the bonding method have uneven distribution of abrasive grains and are not firmly bonded; the abrasive grain phase distribution of the composite coating method is difficult to control and easy to fall off, the sphericity of the magnetic abrasive material of the sintering method is not high, the uniformity of the grain diameter is poor, the wettability requirements of the abrasive grain phase of the casting method and the ferromagnetic phase are high, the grain diameter distribution is inconsistent, the cutting edge of the abrasive grain phase of the plasma melting method is passivated, the grain size distribution range of the magnetic grains of the atomization rapid solidification method is wide, and a certain difference exists between the cutting edge passivation and the grain size distribution range of the magnetic abrasive material and the.
Disclosure of Invention
The invention aims to provide a method for preparing a magnetic abrasive material by supercritical carbon dioxide assisted plasma spray, which comprises the steps of heating ferromagnetic phase powder to be molten by radio frequency induction plasma to form spherical molten drops with consistent granularity; and then, the supercritical carbon dioxide fluid containing hard particle abrasive grain phase is used for jetting the ferromagnetic phase metal molten drops, and the rapid expansion and atomization cooling characteristics of the supercritical carbon dioxide are fully utilized, so that the abrasive grain phase particles are uniformly distributed and firmly embedded on the spherical ferromagnetic phase matrix, and the magnetic abrasive material with high sphericity, strong binding power, consistent particle size and uniformly distributed abrasive grain phase is prepared.
The method provided by the invention specifically comprises the following steps of ferromagnetic equivalent plasma spray, preparation of abrasive particle phase supercritical carbon dioxide mixed fluid and atomization spraying of the mixed fluid:
(1) plasma fusion of ferromagnetic phase: establishing a stable plasma torch by a radio frequency induction plasma generating device; carrying gas is sprayed into the plasma torch from the charging gun handle by 800-1200 mesh iron powder along the axial direction; the iron powder is rapidly heated to be molten and is ejected from the outlet of the plasma torch in the form of tiny liquid drops with high sphericity.
(2) Preparing a grinding phase supercritical carbon dioxide mixed fluid: putting the alumina hard abrasive particles of 10-50 meshes into a high-pressure reaction kettle; introducing carbon dioxide gas into the reaction kettle by using a double-plunger micro pump; heating the reaction kettle by a heating sleeve to ensure that the pressure and the temperature in the kettle are stabilized at 10-15MPa and 40-60 ℃ respectively, and carbon dioxide is converted from a gaseous state to a supercritical state; and stirring the supercritical carbon dioxide and the hard abrasive particles for 30min by using a stirring device in the reaction kettle to obtain the abrasive particle phase supercritical carbon dioxide mixed fluid.
(3) Atomized spraying of mixed fluid: conveying the abrasive-phase supercritical carbon dioxide mixed fluid to an annular nozzle through a pipeline; adjusting the installation angle of the nozzle, and spraying the abrasive particle phase particles to ferromagnetic phase molten drops which are sprayed out from an outlet of the plasma torch and move along the axial direction of the annular nozzle; under the action of ultra-strong permeation and rapid expansion of supercritical carbon dioxide, abrasive particle phase particles easily overcome the agglomeration force and are uniformly distributed on the surface of a ferromagnetic phase; under the action of Joule-Thomson effect of supercritical carbon dioxide, the binding force between the abrasive phase and the ferromagnetic phase is obviously enhanced.
(4) And the ferromagnetic phase molten drops with the abrasive grain phase embedded on the surface enter a magnetic abrasive reaction chamber for cooling, and then enter a gas-solid separation chamber for separation and collection, so that the magnetic abrasive with high shape, strong bonding force, consistent particle size and uniformly distributed abrasive grain phase is obtained.
The method for preparing the magnetic grinding material by the supercritical carbon dioxide assisted plasma fusion injection has the following advantages and effects:
different from the traditional plasma melting method which obtains the magnetic abrasive material by heating and melting the mixed powder of the iron matrix and the hard abrasive particles, the invention only utilizes radio frequency induction plasma to heat ferromagnetic phase powder and supercritical carbon dioxide fluid to jet the hard abrasive particles, and the abrasive particles collide with ferromagnetic phase molten drops in a very short time, the abrasive particles are low in heating temperature and short in heating time, the exposed part is embedded on the surface of ferromagnetic phase metal along with the solidification of a contact interface after being not melted, and the cutting edge of the magnetic abrasive particle phase molten drop is free from abrasive particle phase spheroidization and cutting edge passivation caused by the traditional plasma melting method; even if diamond PCD is used as the abrasive grain phase material, the cutting edge damage phenomenon caused by chemical reaction of PCD and iron element is weakened or avoided due to the characteristics of no direct heating by radio frequency plasma, short contact time with ferromagnetic phase molten drops and the like.
Different from the traditional atomization and rapid solidification method which utilizes fast moving gas to forcibly inject the hard particles of the abrasive particle phase into the molten ferromagnetic phase so as to atomize the molten liquid mixed with the hard abrasive particles into tiny molten drops, the method adopts supercritical carbon dioxide to atomize and spray the particles of the abrasive particle phase instead of atomizing the molten drops of the ferromagnetic phase; after the abrasive particles are sprayed out from the nozzle, the rapid expansion of the supercritical carbon dioxide is caused by the rapid change of the pressure difference, the attraction among the abrasive particle phases is easily overcome, and the problem that the abrasive particle phases are not uniformly distributed on the surface of the ferromagnetic phase metal due to the agglomeration of hard abrasive materials in the traditional atomization and rapid solidification method is avoided; even if a hard abrasive with poor fluidity and strong adsorbability is adopted, under the action of super-strong permeation and rapid expansion of supercritical carbon dioxide, the phenomena of abrasive particle agglomeration and inconsistent distribution are difficult to occur on a ferromagnetic phase.
Compared with the magnetic abrasive prepared by the traditional methods of plasma melting, atomization rapid solidification and the like, the magnetic abrasive has wider particle size distribution range, the pressure and the temperature of supercritical carbon dioxide can be adjusted, and the jet speed of supercritical carbon dioxide jet flow is controlled, so that the speed of hard abrasive particles impacting ferromagnetic phase molten drops is lower than the critical speed of molten drop damage, and the problem of particle size reduction caused by molten drop splitting is avoided; in order to ensure the depth of the hard abrasive particles embedded into the ferromagnetic phase and improve the binding force of the hard abrasive particles and the ferromagnetic phase, even if the injection speed of the abrasive particles is higher than the critical speed, the invention can also adjust the injection direction of the supercritical carbon dioxide, control the angle of the abrasive particles impacting the ferromagnetic phase molten drop, weaken the impact force causing the molten drop to be broken, and also effectively control the consistency of the particle size of the ferromagnetic phase.
According to the method for preparing the magnetic abrasive by the supercritical carbon dioxide assisted plasma spray, iron powder or iron-based alloy powder with different particle sizes can be selected as a ferromagnetic phase according to needs, and hard abrasives of different types and different scales are selected as abrasive phases, so that the multi-scale composite magnetic abrasive with higher polishing quality, fewer polishing defects and wider application occasions can be prepared.
Drawings
Fig. 1 is an SEM photograph of a magnetic abrasive prepared by supercritical carbon dioxide assisted plasma spray.
Fig. 2 is an XRD spectrum of the magnetic abrasive prepared by supercritical carbon dioxide assisted plasma spray.
Detailed Description
The invention discloses a method for preparing a magnetic abrasive by supercritical carbon dioxide assisted plasma spray, which comprises the following preferred specific implementation modes: generating an excitation electromagnetic field by using a radio frequency induction plasma generator and establishing a stable plasma torch, wherein argon is used as working gas; 1000-mesh iron powder is axially sprayed into a plasma torch by a charging gun carrying argon gas(ii) a Ferromagnetic powder absorbs a large amount of heat in a plasma torch within a very short time to be rapidly melted and is ejected from an outlet of the plasma torch at a very fast speed, and the technological parameters of the radio frequency plasma are as follows: electromagnetic frequency of 3.5MHz, argon as working gas, and central gas flow of 1.5m3H, side gas flow 3 m3H, the power is 100kW, and the injection amount of the iron powder is 100 g/min; putting 20-mesh alumina hard abrasive particles into a high-pressure reaction kettle; introducing carbon dioxide gas into the reaction kettle by using a double-plunger micro pump; heating the reaction kettle by a heating sleeve to ensure that the pressure and the temperature in the kettle are stabilized at 12MPa and 50 ℃ respectively, and carbon dioxide is converted from a gaseous state to a supercritical state; stirring the supercritical carbon dioxide and the hard abrasive particles for 30min by using a stirring device in the reaction kettle to obtain an abrasive particle phase supercritical carbon dioxide mixed fluid; conveying the abrasive-phase supercritical carbon dioxide mixed fluid to an annular nozzle through a pipeline; adjusting the installation angle of the nozzle, and vertically injecting the abrasive particle phase particles to ferromagnetic phase molten drops which are injected from an outlet of the plasma torch and axially move along the annular nozzle; under the action of ultra-strong permeation and rapid expansion of supercritical carbon dioxide, abrasive particle phase particles easily overcome the agglomeration force and are uniformly distributed on the surface of a ferromagnetic phase; and the ferromagnetic phase molten drops with the abrasive grain phase embedded on the surface enter a magnetic abrasive reaction chamber for cooling, and then enter a gas-solid separation chamber for separation and collection, so that the magnetic abrasive with high shape, strong bonding force, consistent particle size and uniformly distributed abrasive grain phase is obtained.
The prepared magnetic abrasive is washed with absolute ethyl alcohol and deionized water and dried in vacuum, and the microstructure and chemical composition are measured by using a scanning electron microscope and an X-ray diffractometer, as shown in fig. 1 and 2. The prepared magnetic grinding material has a regular spherical structure, and the hard grinding material is uniformly and densely embedded in the superficial layer of the metal matrix, the cutting edge protrudes out of the metal matrix and is firmly combined with the metal matrix; through phase analysis of the magnetic abrasive, the prepared magnetic abrasive consists of a matrix phase and an alumina abrasive phase, elements in an iron matrix and abrasive elements are not diffused, and the bonding type of an interface is mechanical bonding caused by rapid cooling solidification. It is to be understood that the examples described herein are for purposes of illustration only and are not to be construed as limitations of the present invention.